The invention relates to a multi-voltage electrical system for a vehicle.
In a known version of this kind (U.S. Pat. No. 5,451,823), the PLUS and MINUS diodes of a rectifier unit are each secured to a so-called heat sink and electrically connected to it via a housing terminal. The heat sinks are secured in sandwich fashion with an intervening insulator plate on the end face of a bearing plate for a rotary current generator. The lower heat sink is mounted electrically and thermally conductively on the end face of the bearing plate. A circuit board is located on the upper heat sink and has a number of bus bars--embedded in the plastic of the circuit board, for the connection of one PLUS diode and one MINUS diode each on the one hand and for the winding ends of the rotary current winding in the stator of the rotary current generator on the other. This rectifier unit is held together by rivets and is secured with screws to the rotary current generator. For cooling of the upper, curved heat sink, this body is provided with many cooling slits, located side by side in the region of its inside circumference, which are oriented axially to the axis of the electric machine and through which an axial cooling air stream is drawn in from outside to a fan secured to the rotor of the generator. The cooling air blown radially outward by the fan in a known manner through slits on the outer circumference of the bearing plate.
In this known version, it is disadvantageous that the openings, provided for the cooling air to flow through, in the upper heat sink of the unit have relatively small cooling surface areas for heat dissipation, and thus a relatively thick upper heat sink is needed in order to provide an adequate cooling surface area at the cooling air openings. Because of the attendant accumulation of material required, the upper heat sink used here is correspondingly expensive and heavy. Furthermore, to attain a large cooling area for the cooling air flow, the openings in the heat sink are embodied as narrow, radially extending slits, which in turn present relatively high air resistance to the cooling air stream. As a result, the air volume aspirated through these slits is small, and thus the cooling action is also only slight. Using higher-power fans leads to greater expense and increased flow noise.
A further disadvantage of the known generators of this type is that in the rectifier unit, the heat is carried from the MINUS diode bases to the MINUS heat sinks. From there some of the heat is given up--as noted above--directly to the air, while some is transferred via fastening points to the bearing plate and from there is given up to the air. As a result, most of the dissipated heat is absorbed by the air before it enters the interior of the generator. In generators where conversely the MINUS heat sink rests flat on the slip ring bearing plate, the heat flows from the MINUS diode base to the air via the MINUS heat sink and the bearing plate. However, this version requires an especially rigid heat sink and machined bearing faces of large area.